1. Field of the Invention
Embodiments of the present invention generally relate to a test system for substrates and a method of testing substrates, in particular to test systems for glass substrates and a method of testing electronic structures on glass substrates. More particularly, the invention relates to an integrated testing system for large area substrates in the production of flat panel displays. Specifically, they relate to a voltage compensation assembly, an apparatus for testing electronic devices on a substrate, a method for active voltage compensation, and a method for testing a plurality of electronic devices on a large area substrate
2. Description of the Related Art
Flat panel displays have recently become more and more common and are widely used as a replacement for the cathode ray tubes displays. Generally, different types of flat panel displays can be used. For example, active matrix liquid crystal displays (LCD's) are one type of displays. Further, displays including OLEDs or plasma displays may also be used. An LCD, OLED display or plasma display has several advantages over the CRT, including higher picture quality, lighter weight, lower voltage requirements, and low power consumption. The displays have many applications in computer monitors, cell phones, televisions and the like.
Generally, electronic control of pixel elements on a substrate is provided for LCDs, OLEDs or Plasma displays. For example, an active matrix LCD includes a liquid crystal material sandwiched between a thin film transistor (TFT) array substrate and a color filter substrate to form a flat panel display. The TFT substrate includes an array of thin film transistors, each coupled to a pixel electrode and the color filter substrate includes different color filter portions and a common electrode. When a certain voltage is applied to a pixel electrode, an electric field is created between the pixel electrode and the common electrode, orienting the liquid crystal material to allow light to pass therethrough for that particular pixel.
During manufacturing of displays testing of the flat panel substrate is required to determine the operability of the individual pixels. Voltage imaging, charge sensing, and electron beam testing are some processes used to monitor and troubleshoot defects during the manufacturing process. For example, during electron beam testing, the response of a pixel is monitored to provide defect information. In one example of electron beam testing, certain voltages are applied to the pixel electrodes, and an electron beam may be directed to the individual pixel electrodes under investigation. Secondary electrons emitted from the pixel electrode area are sensed to determine the electrode voltages. Other testing procedures might be provided for LCD displays, such as TFTs, OLED displays and plasma displays. Generally, for testing procedure, a substrate carrying the display or a portion of the display is disposed in or on a testing apparatus.
The size of the processing equipment as well as the throughput is a great concern to flat panel display manufacturers, both from a financial standpoint and a design standpoint. Thereby, flat panel displays or substrates for flat panel displays and other large area electronic equipment have to be carefully treated in order to not decrease the yield of the manufacturing process. Current flat panel display processing equipment of generation 8.5 (G 8.5) generally accommodates large area substrates up to about 2200 mm by 2500 mm and larger. The demand for larger displays, increased production and lower manufacturing costs has created a need for improved testing systems that can improve the yield of substrates found to meet the production criteria.
Therefore, there is a need for a test system to perform testing on large area substrates and methods for testing of large area substrates whereby an improved substrate treatment can be provided.